1. TECHNICAL FIELD
The present invention relates generally to a driving power control system for a vehicle and more particularly to a driving power control system for a vehicle which keeps an unchanged driving power after the shift by an automatic transmission.
2. PRIOR ART
Prior art driving system, as shown in FIG. 26, allows an automatic transmission ATM to convert the output from an engine EG into a driving power. Within the automatic transmission ATM, a throttle valve THVO controls throttle pressure in response to the operating degree of an accelerator (pedal) ACP, and a control circuit COM drives solenoid valves No. 1 and No. 2 (S1 and S2) according to a shifting pattern shown in FIG. 27. A throttle position (opening) sensor THPS and a vehicle speed sensor SS therefor sense the opening of the throttle valve THVA and a vehicle speed representative of the speed of a driven output shaft OPS, which is provided with the automatic transmission ATM, respectively. The shifting pattern is stairs-like in FIG. 27, wherein solid and broken lines represent upshifting characteristic and downshifting one, respectively.
Published Unexamined Japanese Patent Application No. 58-174749 discloses a control system for the driving power from the automatic transmission ATM, which reduces upshifting shocks. The system controls the energy emitted from a drive line by reducing the output from the engine EG by limiting the specific volume of intake air thereof.
Published Unexamined Japanese Patent Application No. 59-99046 further discloses a control system, which controls the speed of varying the opening of the throttle valve THVA in response to the increased response of the speed of the engine EG. The control is executed in response to a required gear position and the operating degree of the accelerator ACP.
These, however, prevent neither of the following shifting shocks; one is caused by the stairs-likely reduced driving power in the case of upshifting, and the other is caused in the opposite case, both being shown in FIG. 28. The latter, which generates when the accelerator ACP operates to such a degree that the throttle opening exceeds a value plotted on a downshifting line shown in FIG. 27, is especially big. Since it is caused by both increased driving torque due to the higher gear ratio and increased torque from the engine EG due to the higher operating degree of the accelerator ACP after a shift.
Another problem is that stairs-like increased acceleration is unavailable during the shift by the automatic transmission. When the accelerator ACP operates in fourth gear, as shown in FIG. 29, for example, acceleration increases gradually to G1. However, during a shift to third, acceleration increases from G1 to G2 abruptly, thus the acceleration therebetween fails to be stably utilized. It further causes a problem of frequent shifts.